1. Field of the Invention
The present invention relates to a monolithic resonator for use in a vibrating beam force sensors such as a vibrating beam accelerometer (VBA) and a vibrating beam pressure transducer (VBPT) in which the proof mass, the proof mass suspension system or the pressure force suspension system and the resonator are made from a single piece of quartz crystal.
2. Discussion of Prior Art
The sensing element or resonator is a force-sensitive, vibrating beam. The vibrations of the vibrating beam are sustained by the combined interaction of the electrode pattern plated on the beam, the piezoelectric properties of the quartz crystal material and the electrical energy supplied by the electronic oscillator circuit. When the vibrating beam experiences axial tension, its vibration frequency increases and, conversely, when the beam experiences compression, its vibration frequency decreases. The advantages of such a sensing element in an accelerometer application include a direct digital output as well as good stability and low temperature sensitivity due to the properties of quartz crystal. The advantages to be gained by fabricating the structure from a single piece of quartz crystal include low cost, elimination of many assembly operations, elimination of joints, and compact size.
Single piece VBA's or VBPT's, per se, are known in the art, for example, see U.S. Pat. No. 4,804,875 which discloses a monolithic piezoelectric structure in both single and dual vibrating beam configurations. See also, as representative examples, U.S. Pat. Nos. 4,658,174; 4,658,175; 4,656,383; 4,446,394; 4,445,065, 3,479,536 and 3,470,400.